Cycles/ CUDA out of memory (sometimes)
Memory on the left is your VRAM and on the right it's your RAM.

441Mb of VRAM is not much though, what's your GPU? You probably want to upgrade if you are going to use it to render.

You can also try to optimize your scene, easiest way to do this is to bake as much things as you can, lower texture resolution and your number of polygons, create instances instead of duplicating object data. Also you can probably reduce lights bounces but I'm not certain this would help. 

That or just render with your CPU (it will take longer but will store data in RAM instead of VRAM). How much RAM do you have?

Google 'Cycles Optimization VRAM' for more info on the subject.

Here you'll find a way to launch Blender in debug mode to troubleshoot memory usage: How do I see what is using Memory?